The disclosure relates to a method for operating a hydraulic brake system of a motor vehicle, wherein the brake system has at least one wheel brake, one brake pedal device and at least one actuatable pressure generator for hydraulically activating the wheel brake as well as an electromechanical actuator which is assigned to the wheel brake and has the purpose of activating the wheel brake, wherein the pressure generator and the actuator can each generate a force for moving a brake piston of the wheel brake for the activation thereof, wherein the pressure generator and the actuator are actuated in such a way that together they generate a total clamping force.
Furthermore, the disclosure relates to a device for operating such a brake system and to a brake system of this type.
The method, device and brake systems of the type mentioned at the beginning are already known from the prior art. Hydraulic brake systems are usually employed as a service brake in motor vehicles, with which service brake the driver of a motor vehicle can set a desired braking torque at the wheels of the motor vehicle. For this purpose, a brake pedal device has a brake pedal which can be activated by the driver in order to generate a hydraulic pressure in the brake system, if appropriate using a brake booster and a masterbrake cylinder. It has also become known also to use hydraulic brake systems as handbrakes or parking brakes. It is also known to assign, in addition to the hydraulic brake system, an electromechanical actuator to one or more wheel brakes which interacts with the respective wheel brake in order to move a brake piston into a brake application position and hold it there. By means of self-locking transmission between the drive and the brake piston, the brake piston can be locked in the brake application position without further energy having to be consumed. The transmission is usually a self-locking spindle/spindle nut arrangement. The latter is driven by an electric motor of the actuator. In the brake system, in which the brake application force for the handbrake function is made available solely by the electromechanical actuator, methods are already known for monitoring or ensuring the brake application force. It is also known to safeguard the hydraulic portion on the basis of intrinsic variables of the electromechanical actuator, wherein the functional capability of the hydraulic part of the brake system is inferred as a function of at least one electrical characteristic variable of the actuator. However, until now this has only been possible when the actuator and pressure generator are actuated simultaneously.